This invention relates to crankshaft bearings for internal-combustion engines that are made of a light metal alloy. The crankshaft bearings are formed by the bearing sections of the crankcase and the bearing caps, the bearing caps being preferably mounted on a bridge. The bearing sections and the bearing caps are joined together by means of screws or bolts set apart from each other.
Known crankshaft bearings of the aforementioned type (EP-PS-European Pat. No. 003 865), because they are made of a light metal alloy, reduce the weight of an internal combustion engine. However, this weight reduction is achieved only at the cost of considerably increased mechanical noise. This noise is a result of the relatively extensive expansion of the light-metal crankshaft bearings at the operating temperatures of an internal combustion engine. The expansion causes the bearings to leave their originally intended tolerance zone which results in a bearing clearance occurring between the crankshaft journal and the bearings, thereby increasing mechanical noise.
In order to avoid this problem, it is known (DE-OS-German Published Unexamined Patent Application No. 31 35 863) to pour into the bearing cap of the crankshaft bearing a core of iron metal which is formed by a strip and extends transversely to the bearing cap at a distance from the crankshaft journal. This method of construction, however, does not achieve the desired reduction of noise, since the light-metal bearing surface of the bearing cap still expands and the strip, because of its low reinforcing and supporting function, does not prevent an effective enlargement of the bearing clearance.
Therefore, an objective of this invention is to provide crankshaft bearings for internal-combustion engines which, while maintaining their favorable weight, are constructed so as to avoid noise-increasing changes of the bearing clearance. This objective is achieved by providing a core of iron metal poured into at least the bearing caps, this core exhibiting lugs for bores penetrated by attaching screws and a transverse part extending between the lugs and forming a bearing area directly surrounding a crankshaft journal. In preferred embodiments the bearing caps are shaped so as to provide a toothed interlock of the core and bearing caps and the bridging transverse part includes openings for accomodating connectors extending between respective cores and bearings caps.
In certain preferred embodiments a further core of iron metal is provided in an opening of the crankcase, this further core being also penetrated by the bolts extending through the core sections in the bearing caps and held at the crankcase.
The advantages achieved by means of this invention are that considerable stiffness is supplied to the bearing caps by the cores of iron metal which reaches around the bearing surface and also by the lugs and the transverse part. The added stiffness to the bearing cap (which is a component of a light-metal bridge reinforcing the crankcase), permits an acceptable increase of the bearing play that will not cause any disturbing bearing noises. This stiffness is promoted even more by supporting the lugs at the bearing sections and by the tensioning means of the screws (screw nut, screw head) at the lugs. Through the selection of the cross-section, the core, having a relatively light weight, will have high stability. A good connection between the bearing cap and the core is achieved by means of the passage opening and the expansions and recesses forming the toothing along the lugs.
By means of a core provided only in the bearing caps, a considerable reduction of noise is attained in internal combustion engines which have a light-metal crankcase or light-metal bearings. This noise-reduction can be further optimized when a further core section is also provided in the bearing sections of the crankcase according to certain preferred embodiments of the invention. A good connection is assured in this case by screwing those screws holding the bearing cap in position into the thread of the bearing section and into its further core section.